Adsorptive removal of heat stable salt anions from industrial lean amine solvent using anion exchange resins from gas sweetening unit

• Anion exchange resins were tested to remove major anions from amine solution.
• Solvent-to-resin ratio administers a prime effect on the adsorption process.
• The maximum anions uptake was 528.24 mg/g.
• The breakthrough time was 7 h.

The formation of heat stable salts (HSS) in natural gas sweetening unit causes many problems such as corrosion, foaming and fouling of the equipment. HSS being resistant to heat cannot be removed from the solvent by simple heating in the regenerator, hence demanding new approaches for HSS removal from aqueous solution of lean amine (methyldiethanolamine) solvent. In this study, four different grades of commercial anion exchange resins designated as Resins A–D were tested to remove major organic acid anions, sulfates and nitrates from direct raw industrial lean amine solution. Based upon the best percentage removal data, Resin C was selected for elaborate batch and continuous ion-exchange adsorption studies. The solvent-to-resin ratio was seen to administer a prime effect on controlling the adsorption process. SEM and FTIR analysis on Resin C mapped the surface morphology changes and interaction of HSS adsorption process over the resin. The equilibrium batch sorption studies for organic acid anions removal were fitted into Langmuir, Freundlich, Temkin and Dubinin–Radushkevich (D–R) model isotherms to obtain the best fitted model. It was observed that Langmuir equilibrium isotherm best explained the ion exchange process. The Langmuir model predicted qmax value of 528.24 mg/g. The sorption kinetics obeys pseudo-first-order having rate constant 1.3763 min−1. The negative values of Gibb's free energy explain spontaneity of the reaction with exothermic heat of adsorption (ΔH = −9.428 kJ/mol) for the removal of organic acid anions using anion exchange resins. The breakthrough curves for removal of organics in column bed with 2.54 cm column diameter and flow rate of 5 ml/min was achieved within 7 h.